1. Field of the Invention
The invention relates to a recording material having, in sequence, a support, a radiation-sensitive layer and a silicone layer. It furthermore relates to a process for the production of a printing plate for driographic offset printing from the recording material.
2. Description of the Related Art
Recording materials from which driographic (i.e., water free) offset printing plates can be produced are already known. Thus, Great Britain Patent GB 1,399,949 discloses a positive-working material having a support, a radiation-sensitive layer which takes up printing ink, a silicone layer which repels printing ink and preferably also a transparent protective film. The radiation-sensitive layer comprises, as essential constituents, a photopolymerizable, ethylenically unsaturated monomer or oligomer having a boiling point of above 100.degree. C., a photoinitiator and generally also a binder. The binder is preferably a vinyl polymer or copolymer (such as polyvinyl acetate, polyvinyl alcohol, polyvinylbutyral, polyvinyl butyl ether, polyvinyl chloride or polyethylene), a polyether (such as polyethylene oxide or polypropylene oxide), a polyamide, a polyester, a cellulose derivative, a urea-formaldehyde resin, an alkyd resin, a melamine-formaldehyde resin or a phenol-formaldehyde resin. In the exposed areas of the radiation-sensitive layer, the monomer or oligomer is polymerized, causing it to adhere to the silicone layer. The recording material is then treated with a developer solution. During this treatment, the silicone layer swells to a greater extent in the unexposed areas and can be removed by brushing or similar measures. In the exposed areas, by contrast, the silicone layer remains adhering to the photosensitive layer. The adhesion between the photosensitive layer and the silicone layer can be further increased by heating or by full-area exposure. At the same time, the photosensitive layer is cured in the originally unexposed areas, which reduces the scratch sensitivity of the driographic printing plates and allows a longer print run.
The recording material according to European Published Application No. EP-A 0 394 923 likewise comprises a support, a photosensitive layer and a silicone layer. The photosensitive component here is a diazonium salt polycondensation product. The photosensitive layer contains, as a further essential component, a polymeric binder containing units of an ester containing aliphatic hydroxyl groups, or of an amide of acrylic or methacrylic acid. It is in general a polymer containing units of a hydroxyalky 1 (meth)acrylate or (meth)acrylamide. In addition, it may also contain units of other monomers. Examples thereof are monomers containing aromatic hydroxyl groups (such as N-(4-hydroxyphenyl)acrylamide or -methacrylamide, 2-, 3- or 4-hydroxystyrene, (2-, 3-or 4-hydroxyphenyl)acrylate or -methacrylate). Furthermore, the monomers may also be a,b-unsaturated carboxylic acids, substituted alkyl acrylates or -methacrylates, vinyl ethers (such as ethyl vinyl ether, butyl vinyl ether or phenyl vinyl ether), styrenes, vinyl ketones, olefins, N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine, acrylonitrile or methacrylonitrile. The proportion of hydroxyl groups in the binder (this is apparently taken to mean the proportion of units containing aliphatic hydroxyl groups) is said to be from 5 to 100% by weight, preferably from 20 to 100% by weight, since otherwise the adhesion between the radiation-sensitive layer and the silicone layer is inadequate. After imagewise exposure, the recording material is developed using an aqueous solution containing polar solvents (such as alcohols, ethylene glycol monoalkyl ethers, ketones or esters), alkaline compounds, surfactants and aliphatic, aromatic or halogenated hydrocarbons (such as hexane, heptane, toluene or xylene). This removes the unexposed areas of the radiation-sensitive layer together with the overlying areas of the silicone layer. In addition, a primer layer is arranged between the aluminum support and the radiation-sensitive layer. This is not removed during development. During printing, the ink is transferred from the primer layer, while the areas of the silicone layer which remain repel the printing ink.
The known recording materials for the production of driographic printing plates require organic solvents during development. However, this is disadvantageous for reasons of occupational safety and environmental protection. Disposal of the spent developer solutions is complex and costly. The present invention is directed to overcoming or at least reducing the above problem.